The rapidly increasing contribution of renewable energy sources in the electricity grid requires development of efficient energy storage methods. Electrolysis can play an important role for energy storage purposes.
In particular, efficient transformation of excess electricity into fuel, such as hydrocarbons or hydrogen gas, may offer a sustainable solution for the energy requirements of the transportation system without the need for a change in transportation technology and infrastructure.
An electrolysis cell is generally characterized by three component parts: an electrolyte and two electrodes, i.e. a cathode and an anode. When driven by an external voltage applied to the electrodes, the electrolyte conducts ions that flow to and from the electrodes, where the reactions take place. The cathode and anode are characterized by the reduction and oxidation of the species that are present in the cell, respectively. For example, in water electrolysis with an aqueous alkaline electrolyte, water is reduced to hydroxide ions and hydrogen gas at the cathode, while hydroxide anions are oxidized to oxygen gas at the anode. Thus, water electrolysis is a method that uses electricity to drive the otherwise non-spontaneous chemical reaction of dissociation of water into oxygen and hydrogen gas.
Co-electrolysis is a method that uses electricity to drive the otherwise non-spontaneous chemical reaction of producing hydrocarbons or syngas by electrolysis of carbon dioxide and water.
Currently, the research and development of electrolysis cells focuses either on operation at elevated temperatures, i.e. above 500° C., or at low temperatures, i.e. below 150° C.
WO 2006/066918 discloses new proton conducting, solid electrolytes in the form of rare earth orthoniobates or orthotantalates being able to operate in electrolysis cells at high temperatures and in a humid atmosphere.
Ion conductivity has previously been described at high and intermediate temperatures in a number of oxides and oxidic materials.
However, there are no solid conductors or other suitable conductors working satisfactory in the temperature range between 200 and 500° C., i.e. within the range of the “Norby gap”, i.e. Norby, Solid State Ionics 125, (1999) 1-11. Generally high temperature electrolysis is more commonly pursued with oxide ion conductors, generally limited to temperature above ca. 500° C.
On the other hand Proton Exchange Membranes (PEMs) are limited to operation below ca. 150° C. and require expensive electrocatalysts, such as Pt. Accordingly, there is a need for electrochemical cells that are able to efficiently and reliably operate within intermediate-low temperatures.
Hence, an improved electrochemical cell would be advantageous, and in particular a more efficient and/or reliable electrochemical cell that is able to operate within intermediate-low temperatures would be advantageous.
Further, an improved electrolysis and co-electrolysis cell that can reversibly operate as a fuel cell would be advantageous.